Manufacturers of composite doors strive to create a door skin that closely resembles a real wood door. They must also strive to reduce the cost of manufacturing such a door. Manufacturers have implemented a variety of manufacturing processes to achieve these sometimes conflicting goals.
For example, U.S. Pat. No. 6,485,800 to Littschwager, et al (hereinafter “Littschwager”, which is assigned to the assignee of the present application, discloses one process for manufacturing a composite door. In the process disclosed in Littschwager, the door manufacturer creates a silicone mold from an original wood door, referred to as the “plug.” The manufacturer then laminates a skin on the mold. The skins may comprise various materials.
Once the manufacturer has laminated a skin, the manufacturer places a temporary frame on the inner surface of the skin. The frame comprises at least a pair of horizontal pieces, called rails, and at least a pair of vertical pieces called stiles. Typically, when the frame is placed, the manufacturer simply lays the frame down on top of the skin; however, the manufacturer may use adhesive or vacuum pressure to hold the temporary frame in place. The temporary frame acts as a dam when the core material is subsequently applied.
According to the process described in Littschwager, the manufacturer next applies the core material. The core material may comprise various materials, such as wood block, particleboard, medium density fiberboard, or urethane. The manufacturer pours the core material onto the inner surface of the skin within the temporary frame. The core material is carefully measured so that when it rises, the depth of the material will exceed the thickness of the frame. In other words, the core material extends slightly above the frame when the partially completed door is lying on the skin. A machine applies the core, using a timed pouring. For example, in one process, a ninety-second pour provides enough core material for a standard 36″×96″ door to allow for expansion or rise above a one and a half inch frame.
Once the core has cured, but prior to fully cooling, the manufacturer removes the temporary frame. The remaining part, comprising a skin and core, is now ready for machining. Two of these parts are used to assemble a finished door. In a conventional one-and-three-quarter-inch-thick composite door, each part is machined to be seven eighths of an inch thick, including the one-eighth inch skin and three quarters of an inch core.
Once machining is complete, the part (skin and core combination) is removed from the mold (demolded) and placed in a medium density fiberboard (MDF) assembly tray. The assembly tray is a mirror image or the door to be assembled. Every design element of the door is routed into the assembly board so that the skin fits firmly in place.
Final assembly of the composite door involves three components: two machined skin-core combinations and one frame. The manufacturer places a first skin-core combination on the assembly board, applies adhesive to the frame, and sets the frame on the skin-core combination. The manufacturer then applies adhesive to the other side of the frame and places another skin-core combination on top of the frame. The manufacturer then places another assembly board on top of the upper skin and applies pressure or a combination of both heat and pressure to the components to complete the assembly process.
Composite doors manufactured by the method described above as well as by other, conventional methods suffer from several disadvantages. Due to the use of the temporary frame and other factors, the manufacturer has difficulty maintaining close tolerances. As a result, the finished door may not meet quality standards. For example, composite doors manufactured using conventional methods may comprise telegraphing visible or tactile irregularities in the surface of the door. Telegraphing may be evidenced by a noticeable depression or raised area in the transition from frame to core. Since many of the conventional composite doors are pre-finished with a high-gloss topcoat, any irregularities are accentuated, and therefore, the manufacturer cannot sell the door.
Also, in a conventional process for manufacturing composite doors, considerable material is wasted. For example, in a conventional one-and-three-quarter-inch composite door, the temporary frame, or dam, used to hold the core material in place on a skin while it cures is one-and-one-half-inches thick, and the core is poured to a depth greater than this temporary frame. However, the manufacturer must machine the cured core to a thickness of only three quarters of an inch in order to combine one skin-core combination with another to create the one-and-three-quarter-inch composite door. Therefore, more than half of the core material applied to each door section is wasted. In addition, it can be difficult to roll a fiberglass skin accurately.
Addressing telegraphing, also referred to as telescoping, and other quality problems resulting from conventional manufacturing methods results in much wasted time, materials, and money. Doors must be repaired in the field, reworked in the factory, or scrapped. These problems also result in increases in warranty costs as low-quality doors that are shipped to customers must be fixed or replaced. These quality problems and the measures taken to address them all serve to decrease the profitability of manufacturing the doors.
An efficient method of manufacturing a high-quality door is needed.